Electric vehicles, hybrid vehicles, and fuel cell vehicles have been known as electric powered vehicles configured such that a traction motor generating vehicle driving power can be driven using electric power from a vehicle-mounted power storage device represented by a secondary battery. An electric powered vehicle is generally configured to have two types of power storage devices, that is, a high-voltage power storage device (main battery or high-voltage battery) used to supply electric power to a traction motor, and a low-voltage power storage device (auxiliary battery or low-voltage battery) used to supply electric power to auxiliary machines including a controller.
In such a configuration, when a remaining capacity of the high-voltage battery is reduced, the vehicle cannot run as a matter of course. Further, when voltage is reduced due to reduction in a remaining capacity of the low-voltage battery, the controller cannot be operated normally, and thereby there is a possibility that the vehicle cannot run even if the remaining capacity of the high-voltage battery is ensured. Therefore, it is necessary to fully manage the state of charge of the low-voltage battery, in addition to that of the high-voltage battery, and recover the remaining capacity thereof when charging is insufficient.
For example, Japanese Patent Laying-Open No. 2000-341801 (PTL 1) describes a power source device for an electric vehicle equipped with a low-voltage battery and a high-voltage battery, wherein when charging of the low-voltage battery is insufficient, the low-voltage battery is charged from the high-voltage battery through a DC/DC converter.
Further, Japanese Patent Laying-Open No. 7-111735 (PTL 2) describes that, if a remaining capacity of an auxiliary battery becomes insufficient during charging of a main battery when an electric vehicle is in a vehicle stop mode, an output voltage of a DC/DC converter is increased to increase the remaining capacity of the auxiliary battery.
Moreover, Japanese Patent Laying-Open No. 2008-195315 (PTL 3) describes a so-called plug-in hybrid vehicle configured such that a high-voltage battery (main battery) can be charged by a power source external to the vehicle. In addition, Japanese Patent Laying-Open No. 2007-209168 (PTL 4) describes that, when a main battery (main power storage device) is charged by a solar cell, a commercial power source, or the like in a plug-in hybrid vehicle, a battery ECU (Electronic Control Unit) for monitoring the state of the main battery is driven at prescribed intervals to minimize the frequency of activating the battery ECU.
In the configuration of PTL 4, an auxiliary battery can be charged by activating a DC/DC converter during charging of the main battery when the vehicle is in a stop mode. However, in PTL 4, a voltage level of the auxiliary battery is not monitored by the battery ECU, but is monitored by a charging ECU which is always activated during charging of the main battery. In addition, it is described that, if the voltage level of the auxiliary battery becomes lower than a preset threshold value, the charging ECU instructs activation of the DC/DC converter.